FISHERY BULLETIN; VOL. 87, NO. 4, 1989 



roundweight (W to 0.5 lb converted to kg), sex, 

 and date of capture (Hill 1986). 



Anal and Dorsal Fin Spine Analyses 



Anal and dorsal fin spines were collected and 

 prepared for analysis following modified meth- 

 ods of Prince et al. (1984) (Hill 1986). The second 

 anal spine and sixth dorsal spine were selected 

 for age analysis. These were chosen because 

 they were the thickest of the spine complex, and 

 sections taken from spines anterior to these had 

 more prominent core matrices. 



Spine length, defined as the distance from the 

 hole at the center of the condyle base to the spine 

 tip, was measured to the nearest millimeter. 

 Thin cross sections from anal and dorsal fin 

 spines were taken at positions marked at 10% 

 and 5% (respectively) of the spine length from 

 the condyle hole. Spine sections were examined 

 using a compound stereoscope at 63 x and 120 x 

 magnification using either transmitted light or 

 reflected light with a black background. The 

 focus of the spine was defined as the midpoint of 

 the distance between the anterior and posterior 

 portions of the spine along the midsagittal plane. 

 All growth bands were counted and their radii 

 measured with an ocular micrometer along the 

 plane from the focus of the spine to the widest 

 radius of the spine section. Spine radius (anal 

 spine radius = AR; dorsal spine radius = DR) 

 was defined as the distance from the focus to the 

 outside edge of the spine along the same plane. 



Statistical replacement of early missing anal 

 and dorsal spine growth bands in larger fish was 

 accomplished by summarizing band radii statis- 

 tics from smaller, younger specimens in which 

 these early bands were visible. Compiled band 

 radius statistics included spine samples which 

 had at least the first or second band visible. 

 Unpaired i-tests were applied to compare corre- 

 sponding radii between those specimens contain- 

 ing the first and second band and to compare 

 corresponding band radii between sexes. 



Final corrected age estimates were assigned 

 to spine samples missing early bands by compar- 

 ing the radii of the first four visible bands to the 

 means and 95% confidence limits of the compiled 

 data. When the radii of at least three successive 

 bands of the first four visible bands fitted well 

 within the 95% confidence limits of three or four 

 bands of the compiled data, corresponding ages 

 were assigned. The use of this technique to pro- 

 vide final age estimates was based upon the as- 

 sumption that there was a predictable number of 



growth bands per millimeter of radius in the core 

 matrix, and that the first several visible bands 

 were analogous in age to matching bands of the 

 compiled radius data. 



Sagitta Analyses 



Sagitta were cleaned, prepared, and examined 

 following the methods of Radtke (1983) and Hill 

 (1986). Terminology for sagitta orientations is 

 based on Prince et al. (1986). Sagittal otoUth 

 weight (SW) was measured to the nearest 0.005 

 mg. Age assignments were based on combined 

 counts of external gi'owth features present on 

 the sagittae, which included ridges along the 

 anterior rostrum edge on the ventral plane of 

 growth and ridges along the ventral surface of 

 the medioventral and medial planes of growth. 



Previous studies of Istiophorid sagitta have 

 supplemented age estimates based on external 

 features with examination of internal gi'owth 

 features using thin transverse sections and hght 

 microscopy (Wilson 1984; Prince et al. 1986). 

 However, Hill (1986) statistically compared age 

 estimates using external and internal growth 

 features and found no significant difference be- 

 tween the two methods. Therefore, age esti- 

 mates reported in this study were based only 

 upon examination of external features. 



Vertebrae Analyses 



Caudal vertebrae numbers 22 and 23 were re- 

 moved from the area between the posterior por- 

 tion of the second dorsal fin and the base of the 

 caudal fin. These were the only vertebrae which 

 could be removed without lowering the market 

 value of the fish. Vertebrae were simmered for 

 several hours in hot water to remove extraneous 

 tissues and then air dried for at least 72 hours. 

 Vertebral spines and arches were removed, 

 anterior and posterior centra separated, cut 

 longitudinally along the dorsoventral plane, and 

 stored in 95% isopropyl alcohol. 



Vertebral cone depth (CD) (as defined by 

 Johnson 1983), referred to in this paper as cen- 

 trum cone depth was measured to the nearest 

 0.05 mm. Growth rings were observed after 

 carefully peeling away the thin layer of carti- 

 laginous tissue which covers the bony face of the 

 centra. Centrum length, from focus to outside 

 edge, was divided into approximately 5 mm sec- 

 tions and the average number of rings per milli- 

 meter was calculated for each section by count- 

 ing three 1 mm portions in each section. Total 



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